Your findings are correct, but what you heard is correct as well. Early 2008 and earlier MacBook Pros had two USB 2.0 ports, one (on the right I believe) provided more power than the other though. This used to be an issue when attempting to boot to external USB bus powered hard drives, one would have to remember which USB port to use. 2009 and newer models should push more than enough power from all of their USB ports to charge an iPad or boot to a bus powered USB drive. Hope that clarifies.
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Mr RabbitFeb 4 '14 at 14:23

Please notice user51230's answer below. Either port should work, and your screen shot indicated that the USB port was providing 2.1 A current to your iPad.
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Yongwei WuFeb 8 '14 at 8:46

5 Answers
5

You can use either port, the limitation is that only one USB port can provide this higher power level. If you try and charge two iPads at the same time, only one will get provided with the higher power level, and the decision as to which is made on a first-come-first-served basis.

Edit to Add: I forgot to mention that the article says Macs with more than two USB ports may be capable of powering multiple ports (but not necessarily all) at this higher power level. Unfortunately they don't give any further details.

This is a very interesting question. Apple has a support article about powering peripherals through USB. Apple states that each USB port is supplied with up to 900mA at 5V. There have been a few discussions brought up on various forums about port inequality that I have seen, but I don't think Apple has ever addressed any of the claims.

The users who suggested the inequality took it into their own hands to do a bit of testing; I found this very nicely written breakdown.

Sparing the technical details, they ran tests with the front & back USB ports and noticed very small differences. It also suggests that the keyboard/trackpad, memory card reader, and Bluetooth are all connected to the 'front port', and that iSight and IR reciever are connected to the 'back port'. Based on what is connected where and on the numbers from their tests, it appears as though the back port has slightly better performance.

This all said, the difference is so small you'd never notice it charging a device (especially from Apple). Using your iPad with either port is fine. There won't be a noticeable difference.

As suggested, you'll likely get better charging performance by using the wall cube, rather than charging via USB.

Actually, your Macbook CAN provide extra current for apple products. Your screendump indicates that it is charging with 500mA + 1600mA of "Extra Operating Current" which makes a total of 2.1Amps (same as the iPad charger).

Also make sure that the port/device is not being used by Parallels. If you set up your iOS device so it syncs with Outlook on a Windows VM in Parallels, then the current available drops to 500mA. The solution is to temporarily release the device from Parallels, and you will get proper charging ability again.